The detection of many cardiac malfunctions is impeded by the intermittent occurrence of such malfunctions. They may appear only occasionally, masking detection during clinical observation or examination. In other situations it is desirable to be able to monitor heart functioning during normal or near normal subject activity in order to accumulate information on the functioning of the heart in normal and diverse stress situations. Also, in many cases, it is desired to administer medication or therapy to the body during ambulatory conditions.
A portable system capable of being easily placed about the human torso so as to permit a subject under investigation to be monitored in cardiac function during normal or near normal daily activity is shown in our above-identified application. One parameter of interest during such studies and examinations is the cardiac ejection fraction or the relative volume of fluid pumped by the heart on each beat. This can be accomplished by applying a radioactive substance to the subject's blood so that it circulates through the heart, ultimately appearing in the left ventricle. A detector of the radioactive emissions is placed proximate to the heart and senses the level of radioactive decay. Since this is a function of the volume of blood in the left ventricle, the ejection fraction can be determined from the variations in the detected radioactivity over a heart beat cycle.
It is of substantial medical significance to be able to make such measurements while the subject is engaged in normal daily activity in order to detect infrequently occurring irregularities or to document this particular heart characteristic during a range of subject actions. In other cases it is desirable to administer medication or therapy to the subject over time while the subject is ambulatory. In order to avoid the introduction of errors into the measurements, or disturb the administration, it is important the detector or sensor, or applying instrumentation, be located in a position relative to the torso which will not vary significantly during normal subject activity. Any displacement of the detector or other instrumentation during monitoring can introduce a variation in the detected functioning that rendures the detected function, such as ejection fraction, suspect. A disturbance in the applying instrumentation can also result in undesired loss of application or application to wrong areas.